Normally, an imaging apparatus performs a white balance adjustment on an image signal according to a color temperature of a light source. For example, the imaging apparatus corrects with a white balance adjustment in such a way that the white object is shot as white even in a case where the white object is under greenish reflecting fluorescent light or under reddish reflecting incandescent light. A system that automatically performs such a white balance adjustment is called AWB (auto white balance adjustment) system.
The AWB system sets a color-temperature range subject to a white balance adjustment as a color judgment gate. The color judgment gate is considered as a reference based on which a tinged color portion affected by light from a light source of achromatic color is selected from a chromatic color portion. The AWB system integrates pixel data selected by the color judgment gate for each frame, which is divided by the pixel count subject to integration, so as to calculate an average value of the pixel data per each pixel for every frame. For example, when integrating a color-difference signal, the AWB system implements an adjustment using such a white balance gain that the calculated average value becomes zero.
In a conventional system, the color judgment gate is set in such a way that various types of light-source colors, ranging from a light source having a low color temperature to a light source having a high color temperature, are included. In this setting, a color other than the light-source colors may also be included for the selection of the color judgment gate. For example, if an object having hue of low saturation such as a bluish or cyanic tint is shot under the incandescent light, the reddishness resulting from the incandescent light and a blue tinge of the object are balanced as if an achromatic (neutral) color, and may enter the range of color judgment gate. In such a case, even a color other than the light-source color is included in the integration target, resulting in a white balance adjustment in which an ideal point is not reached. In the preceding example of under the incandescent light, the white balance adjustment is performed with a trace of slight reddishness.